CalcKitHow to Use the Water Intake Calculator
Water runs everything: temperature control, digestion, joint lubrication, brain function. Even mild dehydration — just 1–2% of body weight — can cause headaches, fatigue and poor concentration. Yet most people have no idea how much they should actually drink.
Enter your weight and activity level, then press Calculate Water Intake. The calculator uses the widely used guideline of about 35 ml per kilogram of body weight, plus extra for exercise or hot weather. You'll get your target in liters and in standard 250 ml glasses, which makes it easy to track through the day.
Spread your intake across the day rather than chugging it all at once — a glass with each meal plus a few in between gets most people to their target. Coffee and tea count toward hydration (the "coffee dehydrates you" claim is mostly myth for regular drinkers), but water is still the best default.
Increase intake when exercising, in hot climates, when ill, or during pregnancy and breastfeeding. Very high intakes (many liters beyond thirst over a short time) can be harmful, so treat this as a sensible target, not a challenge. If you track fitness, pair this with your numbers from the Calorie Calculator.